1.3 Flashcards
The mass spectrometer
What is Mass Spectrometry used for?
It is used to determine the relative atomic mass (Ar) of an element based on the abundance and mass of its isotopes
What are the four key stages of TOF?
Ionisation
Acceleration
Ion Drift
Detection
Describe the ionisation stage during TOF
The sample is dissolved in a volatile solvent. To create a mist, the solvent is injected into the mass spectrometer via a fine hollow needle. The needle is attached to a high-voltage power supply to inject the solvent, and particles lose electrons. Most atoms will lose only one electron as removing them further is too difficult.
Describe the Acceleration stage during TOF.
The ions are attracted to a negatively charged plate and therefore accelerate towards it using the magnetic field. All the ions will have the same KE however their velocity depends on their mass.
Describe the Ion Drift stage during TOF.
The positive ions will pass through a hole in the charged plate. The ions will enter the flight tube. The time of flight of each ion depends on its velocity (Lighter ions have a shorter time of flight than heavier ions)
Describe the Detection stage during TOF.
The ions will hit a negatively charged detector plate at the end of the flight tube. The ions will gain an electron hence a current is formed. This current is displayed on a computer. The size of the current is proportional to the abundance of the ion.
Which Ions reach the detector plate first?
Lighter Ions
What is the relative abundance of an Isotope?
The proportion of one particular isotope in a mixture of isotopes found in nature?
How is the relative abundance of an isotope represented on a mass spectra?
By the heights of the peaks found on the mass spectra
How can you find the RAM of an element via the mass spectra?
Multiply each isotope abundance by its m/z ratio
Add the values together and divide by 100
What is a high-resolution mass spectrometer used for?
It can be used to find the relative molecular mass of a compound.
